JPS62251710A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens which secures a necessary quantity of back focus, is short in total length and small in aperture, and has a zoom ratio of about 1.5 and excellent performance, by constituting the 1st group of two or more positive lenses and one or more negative lenses and the 2nd group of a positive and negative lenses. CONSTITUTION:The room lens of this invention is composed of the 1st group having a positive refractive power on the object side and 2nd group having a negative refractive power on the camera side and realizes a variable power by changing the interval between the 1st and 2nd groups. The 1st group is composed of two or more positive lenses and one or more negative lenses and the 2nd group is composed of a positive and negative lens from the object side. With this type of zoom lens, it is necessary to make the negative refractive power of the 2nd group higher in order to bring the location of the exit pupil closer to the image side by making the back focus longer. However, when the power of the 2nd group is simply made higher, the aberration produced in the 2nd group becomes larger and excellent aberration correction cannot be expected. Therefore, the second group is constituted of the positive and negative lenses so that the lens system can be miniaturized and, at the same time, excellent aberration correction can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compact zoom lens used in lens shutter cameras and the like.

[Conventional technology]

Conventionally, the main type of zoom lens is composed of a first group with negative refractive power and a second group with positive refractive power, and the magnification is changed by changing the distance between both lens groups (this type is used for reflex cameras). Are known.

Since this type of zoom lens has a negative-positive group configuration, the principal point position approaches the image side, resulting in a long back focus. Therefore, it is easy to secure a space for arranging the flip-up mirror, which is advantageous for an eye reflex camera. However, since the overall length is long, it is not suitable for use in lens shutter cameras, etc., and for cameras that require compactness, such as /Z cameras.

JP-A-57-201 is a conventional example of a zoom lens that is compact enough to be incorporated into a lens-shutter camera.
There is one published in No. 213. This lens is composed of a first lens group with positive refractive power and a second lens group with negative refractive power, and magnification is changed by changing the distance between these lens groups. This zoom lens has achieved a shortened overall length by adopting a so-called telephoto type lens. However, since the outer diameter of the final lens of this zoom lens is large, the overall body tends to increase in size when including the lens drive mechanism.
Furthermore, since the back focus is too short, dirt on the final lens surface tends to deteriorate the image quality.

[Problem that the invention seeks to solve]

In order to eliminate the above-mentioned drawbacks, the present invention provides a lens-shutter camera that secures the necessary amount of back focus, has a short overall length, has a small lens diameter, and has a zoom ratio of about 1.5, making it ideal for lens-shutter cameras with good performance. Our goal is to provide Nasum lenses.

[Means for solving problems]

The zoom lens of the present invention is a lens system that includes a first group having a positive refractive power and a second group having a negative refractive power, and performs magnification by changing the distance between the first group and the second group. It is.

In this type of zoom lens, it is necessary to lengthen the back focus (to bring the exit pupil position closer to the image side).
It is necessary to strengthen the negative refractive power of the group. But just the second
If the power of the group is made strong, the aberrations generated in the second group become sharp, and good aberration correction cannot be achieved.

In the lens system of the present invention, by configuring the second group with a positive lens and a negative lens, the lens system can be made compact and aberrations can be effectively corrected.

That is, the first group is composed of two or more positive lenses and one or more negative lenses, and the second group is composed of a positive lens and a negative lens, thereby achieving the object of the present invention. I tried to get it.

Furthermore, if the following conditions are satisfied, a good zoom lens can be obtained.

(1) 0.5 < f1/ < 1.0 (2)
o, s<'t27 <1.4. t,<.

W ~ (3) 0 < /w < 0.5W (4) 0.1 < /, <0.35, but f+ -
fs is the focal length of the first and second groups, respectively, fW is the focal length of the entire system at the wide-angle end, Dw is the distance between the first and second groups at the wide-angle end, and PW is the exit pupil at the wide-angle end. It is the distance from the position to the final surface.

Each of the above conditions will be explained next.

If the focal length f becomes large beyond the upper limit of condition (1), the total length of the lens system becomes large.When zero or zero focusing is performed using the first group, the amount of extension becomes large, and as a result, the diameter of the front lens becomes large. I have no choice but to become If f+ becomes small beyond the lower limit of condition (1), it is advantageous for compactness, but the occurrence of various aberrations increases, making it difficult to correct pincushion distortion, especially at the wide-angle end.

This would be contrary to the purpose of the present invention. If the lower limit of condition (2) is exceeded and 2( becomes small, the Petzval sum becomes small and the field curvature worsens.

If the interval Dw exceeds the upper limit of condition (3) and becomes a dog, then condition (
Similarly to 2), the exit pupil position moves away from the image plane and the lens system becomes larger. When Dw becomes small beyond the lower limit of condition (3), the refractive powers of the first and second groups become stronger in order to secure a predetermined variable power ratio. As a result, the focal length fl of the first group becomes smaller than the lower limit of condition (1), and as mentioned in the explanation of this condition, the occurrence of various aberrations increases, especially correction of pincushion distortion at the wide-angle end. becomes difficult. Similarly, regarding the focal length f2 of the second group, 1f21 exceeds the lower limit of condition (2) and becomes small, so the Petzval sum becomes small and the field curvature worsens.

Condition (4) relates to the exit pupil position at the wide-angle end. If the upper limit of condition (4) is exceeded, the outer diameter of the second lens group becomes large, which goes against the objective of miniaturization of the present invention. If the lower limit of condition (4) is exceeded, the power of the second group becomes too strong, 1f21 exceeds the lower limit of condition (2), the Petzval sum becomes small, and the field curvature worsens.

If each of the above requirements is satisfied, the lens system can be made smaller, but if the negative lens of the second group is made of a double-concave lens, the principal point of the second group will be closer to the image side, making it even more compact. A zoom lens whose aberrations are well corrected can be obtained.

In addition to the configuration described above, even better aberration correction can be achieved by satisfying the following conditions.

(5) 0.1<smell, <0.5 (6) 0.1<呵, <0.7 (7) 0.1 <”M, <1.0, rb<
0(8) 0.2 < 42 < 0.7, r <
O However, d is the total thickness of the positive lenses existing between the negative lens in the first group and the aperture, ra is the radius of curvature of the image side surface of the negative lens in the first group, and r5 is the sum of the thicknesses of the positive lenses in the first group. The radius of curvature of the surface closest to the image side is the radius of curvature of the surface closest to the image side, and ro is the radius of curvature of the surface of the negative lens in the second group on the object side.

Condition (5) is for correcting field curvature, and if the upper limit of condition (5) is exceeded, it is advantageous for correcting aberrations, but the total length of the lens system becomes short. If the lower limit of condition (5) is exceeded, fluctuations in field curvature due to changes in image height will become too large.

Conditions (6) and (7) are conditions for correcting aberration fluctuations due to zooming. Upper limit of condition (6) 2 conditions (7)
If the lower limit of is exceeded, spherical aberration and field curvature will be insufficiently corrected. If the lower limit of condition (6) exceeds the upper limit of condition (7), spherical aberration and field curvature will be overcorrected.

If the upper limit of condition (8) is exceeded, the field curvature will be insufficiently corrected, and if the lower limit of condition (8) is exceeded, pincushion distortion at the wide-angle end will become too large.

Also, as in Examples 4 and 5 shown later, in the first group or in the second group
By providing an aspherical surface expressed by the following formula in the group, various aberrations, especially curvature of field, can be reduced.

Comatic aberration can be corrected even better.

Here, r is the paraxial radius of curvature or the amount of displacement in the optical axis direction, y is the amount of displacement in the direction perpendicular to the optical axis, and B, E, F, G, and H are aspheric coefficients.

〔Example〕

Next, each example of the zoom lens of the present invention will be shown.Example 1 f = 41.2 to 58.2, -36 to F/6.6r,
=13.086 dl =4.19 n, =1.66680 1
/1=33.04r2=61.292 d2= 1.66 r3"" 62.003 a3= 1.20 n2 = 1.84666
92=23.78r4. :9.800 d+ = 2.95 ry = 18.293 ds = 9.83 n3 = 1.62004
1'3 = 36.25ra" 15.273 da = 2.00 r7=oo (aperture) a, = D r, = 206.959 ds "2.93 n4 = 1.51823
shi, = 58.96rg = -28,114 d, = 2.89 rlQ = -18,949''/ = 0.78, If2 = 0.96W r&/f, = 0.30 屹 = 0.31.

Frost, =-0,47,4=0.48 Example 2 f=41.2~58.2, -06~F/6.6r,
= 14.909 d, = 4.20 nl = 1.73520
ν, =41.08r2=48.227 d2=1.66 r3=-35,192 d3=1. OOnfi =1.80518 ν2
=25.43r4 == 15.566 d4=3.56 rs = 48.548 ds ”2.40 ns =1.56732
shi, = 42.83ra = 65.407 da = 0.15 rt = 47.955 dy = 3.0On4 = 1.59270 j/
, =35.29rg =-20,866d, =2. OO r, =■ (aperture) dQ=I) rlO= 620.617 d+o =2.96 ns =1.53172
5 = 48.90r, 1 = -21,732 dl, = 2.44 r, , = -16,588 d, 2 = 1.1Or + 4 = 1.83400 Shiro = 37.16r, , = 1107.775 D =11.678~2.353 fl/ =0.78, 2/fW=0.99fW
If 1 frost, = 0.48 屹 = 0.17 Example 3 f = 41.2-58.2. F/4.6~F/6.6
ri=”13.269 d+=4.50 nl=1.72825
v, = 28.46r2 = 46.496 d, = 1.34 rs = 111.600 da = 1.0On2 = 1.80518 ν2 = 2
5.43r4 = 8.804 d4=3.15 rs=16.153 ds”10.39 n5=1.54739 5
13=5.3.55ra" 13.748 da" 1,50 r7=o:+(aperture) d7=D r8=-89,808 da=3.0On4=1.63980 17
4 =34.48r@=-23,296 do = 3.13 rto =-16,391 d+o=1.10 n5=1.83400
shi5=37.16r1. =-644,321 D = 11.762-3.263 Example 4 f = 41.2-58.2, F7. ．． 6~F/6
．． 6r, ==14.129 d+ =4.16 1 =1.61293 ci,
=37.0Or2=72.611 d2=1.51 rs=-42,509 da"1.79 n2=1.80518 ν
2=25.43r4 = 13.287 d, = 1.71 r5 =” 23.101 d5=11.48 n3=1.72342 93=
37.95r6 == -20,449 da = 0.71 r2 (aperture) d7=D r8=33.696 da ”3.20 n4 =1.49109
C4=57.0Ore ” 32.105 (Aspherical surface) do ” 2.73 r,. =-18,890 dlo =1.00 ns ”” 1.8160
0 Shi, =46.62rI+=52.554 D =LL389~0.658 fl/ =0.84, 1f2
J w=1.06W C=0.33, /f,=0.38")'=-
0,59,'4=0.43 Aspheric coefficient B=O, E=-0,22901xlOIF=-0,55
44,8X10-7. G=-0,14686X10-
8H=0.16617X10-10 Example 5 f=41.2~582, F/46~''6.6r,=
15.546 ci, =4.85 n, =1.70614
shi, = 41.24r2 = 66.673 d2 = 1.66 r3 = 54.063 d3 = 1.36 12 = 1.80518
ν2 = 25.43r4 = 14.903 (aspherical surface) d4 = 3.96 ra = 26.300 d, ±6.11 13 = 1.59551 ci3 = 39.21r6 = 17.395 da ” 1.50 rt =ω (aperture) d7=D r,: 385.202 ds =2.0On+ =1.51742 M<
= 52.41r, = 24.449 d, = 2.89 r+o = 18.103 dlo = 1.00 na = 1.7995
2 ν5=42.24 shi=0.19,
η, = 0.45f.

"/i, = 0.53. c/f2 = 0.41 Aspheric coefficient B = O, E = 0.26854X10-'F = 0.451
87X10, G=0.92832X10-81 (
=-0,14695X 10-9 where r++r2y... is the radius of curvature of each lens surface, d
l, d2. ... is the wall thickness and air gap of each lens, n4
+n2+... is the refractive index of each lens, and C1. C2.・・・
・ is the Atsube number of each lens.

Among these examples, Example 1 has the lens configuration shown in FIG. 1, with the first group consisting of a positive lens, a negative lens, and a positive lens.
The group was composed of a positive lens and a negative lens. The wide-angle end (ω = 27.7°) of this example, the standard (ω = 23.5°),
The aberrations at the telephoto end (ω=20.4°) are shown in Figure 3 and
As shown in FIGS. 4 and 5.

Example 2 has a lens configuration shown in FIG. 2, with the first group having a positive lens, negative lens, positive lens, and positive lens configuration, and the second group having a lens configuration similar to that of Example 1. The aberrations at the wide-angle end, standard, and telephoto end of this example are as shown in FIGS. 6, 7, and 8, respectively.

Example 3 has a lens configuration similar to Example 1, and the aberrations at the wide-angle end, standard, and telephoto end are as shown in FIGS. 9, 10, and 11, respectively.

Example 4 has the lens configuration shown in FIG. 1, and the ninth surface (r9) is an aspherical surface. The aberrations at the wide-angle end, standard end, and telephoto end of this example are as shown in FIGS. 12, 13, and 14, respectively.

In Example 5, the fourth surface (r4) has the lens configuration shown in FIG.
is an aspherical surface. ra in condition (6) is the radius of curvature at the apex of this first surface. FIG. 15 shows the aberrations of this example at the wide-angle end, standard, and telephoto end.

As shown in FIGS. 16 and 17.

〔Effect of the invention〕

As explained above, the zoom lens of the present invention is a compact lens system with a short overall length and a small outer diameter, and is a zoom lens that is ideal for lens-shutter cameras with good performance.

[Brief explanation of drawings]

Figure 1 is a sectional view of Examples 1, 3, and 4.5 of the present invention;
The figures are cross-sectional views of Embodiment 2 of the present invention, Figures 3, 4, and 5.
The figure is an aberration curve diagram of Example 1, FIGS. 6, 7, and 8 are aberration curve diagrams of Example 2, and FIGS. 9, 10, and 11 are aberration curve diagrams of Example 3. Figures 12, 13, and 14 are aberration curve diagrams of Example 4, Figures 15, 16, and 17.
The figure is an aberration curve diagram of Example 5. Applicant Olympus Optical Industry Co., Ltd.

Claims (1)

[Claims] (1) Consisting of a first group with positive refractive power and a second group with negative refractive power in order from the object side, magnification is changed by changing the distance between the first group and the second group. 1. A compact zoom lens, wherein the first group includes two or more positive lenses and one or more negative lenses, and the second group includes a positive lens and a negative lens from the object side. (2) A compact zoom lens according to claim (1) that satisfies the following conditions. (1) 0.5<f_1/f_W<1.0 (2) 0.6<|f_2|/f_W<1.4, f_2<
0(3)0<D_W/f_W<0.5 (4)0.1<P_W<f_W<35 where f_1 and f_2 are the focal lengths of the first and second groups, respectively, and f_W is the entire system at the wide-angle end , D_W is the distance between the first group and the second group at the wide-angle end, and P_W is the distance from the exit pupil position to the final surface at the wide-angle end. (3) The compact zoom lens according to claim (2), characterized in that the first group or the second group includes an aspherical surface.